DESCRIPTION: (Applicant's abstract) The first long range goal of this project is to understand the neurophysiological mechanisms that contribute to lumbar spine function; the second is to understand the mechanisms by which spinal manipulation affects low back pain. Back pain is very common in our society, and the Department of Health and Human Services recently recommended spinal manipulation as one treatment. The proposed investigation is based on the premise that understanding the neural responses to vertebral joint movement will provide a rational basis for understanding sensory mechanisms contributing to low back pain and the mechanisms by which physical treatment helps relieve back pain. The experiments proposed use a systematic approach to determine the discharge characteristics of lumbar sensory neurons evoked by movement of the lumbar facets. Neurophysiological studies will be performed on single identified sensory neurons to test the following hypotheses: 1) that the discharges of group I, II, III and IV afferents in the lumbar spine are graded with the magnitude and direction of facet joint movement; 2) that the discharges of group III and IV afferents innervating muscles and deep tissues of the lumbar spine during facet joint movement are enhanced by muscle-fatigue induced metabolites, including potassium, lactic acid and diprotonated phosphate; and 3) that the discharges of these afferents is also enhanced by inflammatory mediators, including bradykinin, serotonin, PGE2 and PGI2.